Satellites are used for a wide variety of communications ranging from telephone communications to high speed data communications. A variety of satellites in various orbits are used to provide the different forms of communication. For example, it is common to use communication satellites in geosynchronous orbits. Such geostationary orbits require the insertion of satellites at a location approximately 22,300 miles from earth. Geosynchronous satellites have a circular orbit that lies in the plane of the earth's equator and turn about a polar axis of the earth in the same direction and with the same period as the rotation of the earth such that the satellite is in a fixed position relative to the surface of the earth. Satellites in a geosynchronous orbit have a period of revolution equal to the period of rotation of the earth about its axis.
An earth-based station is used to communicate with a geosynchronous satellite. The earth-based station may have receive-only capability, such as a satellite television receiver, or may include transmission capability to provide a data uplink to a satellite. In either event, the earth-based station must include an antenna that is aimed at the desired satellite. The process of aiming the antenna requires some knowledge of the location of the desired satellite as well as the ability to aim the antenna in the desired direction. This process can be quite time consuming and can require significant technical expertise.
While the process of aiming the antenna can be time consuming, it is typically considered part of a normal installation of an earth-based station at a fixed location and aimed at a geosynchronous satellite. Once the fixed location earth-based station has been pointed towards a particular geosynchronous satellite, it is possible to redirect the antenna on the earth-based station to communicate with other geosynchronous satellites, which have fixed and known locations with respect to each other. For example, a satellite television receiver need only be aligned to detect a first satellite in geosynchronous orbit during an initial installation. Thereafter, the satellite antenna may be moved a known amount to permit reception of broadcast signals from other satellites in geosynchronous orbits and then returned to the known position aiming at the first satellite to receive signals from the first satellite.
The antenna aiming problem is more complex, however, when an earth-based station attempts to communicate with a satellite in a non-geosynchronous orbit, such as a low-Earth orbit (LEO) or a middle-Earth orbit (MEO). Because of their orbits, LEO and MEO satellites will move in the sky when viewed from a fixed ground location and will typically only be in view of a particular earth-based station for a limited period of time. Each time a LEO or MEO satellite comes into range of can earth-based station, the earth-based station must therefore re-aim the antenna to acquire the satellite. Having to continually repoint the antenna to acquire a LEO or MEO satellite that comes into range can be a very time-consuming process that ultimately impacts the total time that the earth-based station may communicate with the satellite. Therefore, it can be appreciated that there is a significant need for a system and method for simplifying and speeding the acquisition of a satellite signal. The present invention provides this and other advantages, as will become apparent from the following figures and accompanying detailed description.